At least one type of system has been proposed for determining the position of moving devices, such as automobiles, along a designated path. That system is disclosed in U.S. Pat. No. 5,162,643 and is generally illustrated in FIG. 1. The system includes a light source 10, which can be in the form of a laser diode, for emitting a light beam 12. One or more retroreflectors 14, 14', 14" are positioned along the intended path of movement for reflecting light transmitted by the laser diode 10. When used to detect the position of a moving vehicle such as an automobile, the retroreflectors 14, 14', 14" can be positioned along the side of the road. The light source 10 mounted on the vehicle could then be directed forward of the vehicle movement to create a field of view.
The system also includes a range detection channel 16 and an angle detection channel 18, both of which are generally illustrated in FIG. 1. The range detection channel 16 and the angle detection channel 18 include a detector for sensing light. The transmitted light from the transmitted light beam 12 reflects off the retroreflectors 14, 14', 14" and returns toward the source 10 in the form of a reflected light beam 20. The detectors in the range detection channel 16 and the angle detection channel 18 sense the light from the reflected light beam so that the angle of the reflected light beam and the distance to the retroreflectors 14, 14', 14" can be determined.
Although the system illustrated in FIG. 1 and described in more detail in the aforementioned U.S. Pat. No. 5,162,643 is quite useful in determining the position of a moving object, such as an automobile, relative to a point or points in advance of the vehicle's direction of movement, it is susceptible of improvements. For example, as illustrated in FIG. 1, the light source 10, the range detection channel 16 and the angle detection channel 18 are positioned vertically above one another. As a result, three different optical axes are provided--the optical axis of the transmitted light beam 12, the optical axis of the portion of the reflected light beam 20 sensed by the detection channel 16, and the optical axis of the portion of the reflected light beam sensed by the angle detection channel 18. Those multiple optical axes necessitate that the housing which encases the various components be sufficiently large to accommodate the components. Thus, the housing cannot be as compact as might otherwise be the case.
Additionally, the system illustrated in FIG. 1 is designed in a way that inhibits the range detection channel and the angle detection channel from sensing a maximum amount of reflected light. As mentioned above, retroreflectors 14, 14', 14" are typically used to reflect the light transmitted by the light source 10. Those retroreflectors 14, 14', 14" are characterized by the fact that they reflect light along a path that is substantially the same as the path along which the transmitted light beam 12 travels. Thus, as seen in FIG. 1, the center portion (i.e., the central axis) of the reflected light beam 20 follows a path that is substantially parallel and coaxial with the central portion (i.e., central axis) of the transmitted light bean 12. However, the reflected light beam 20 diverges as it is reflected off the reflectors 14, 14', 14". The amount of light across the reflected light beam 20 is generally represented by the curve 22 shown in FIG. 1. As can be seen, the concentration or intensity of the light is greatest along the central axis that extends between the light source 10 and the reflector or retroreflector 14 (i.e., a line coaxial with the central axis of the transmitted light beam 12). Those portions of the light beam 20 located further away from that central axis possess lesser concentration. At the outer edges of the reflected light beam 20, the concentration of light is at a minimum.
Since, in the system illustrated in FIG. 1, the range detection channel 16 and the angle detection channel 18 are positioned with respect to the light source 10 in the manner noted, the detector in each channel 16, 18 senses quite a bit less than the maximum amount of reflected light. As a result, the system may not be as sensitive as it might otherwise be insofar as its ability to detect the reflected light.
Given the foregoing, it would be desirable to provide a relatively compact light detection system for detecting the position of a moving object, such as an automobile. In that way, the system can be more readily located at any desired location on the moving object. It would also be desirable to provide such a light detection system that is highly sensitive and accurate, and able to detect a maximum amount of light reflected off a reflector or retroreflector.